[issue24973] CFLAGS for Visual Studio

[Steve Dower]

Steve Dower added the comment:

All environment variables are promoted to MSBuild properties, so if you "set 
IncludeSSL=false" before building then it will show up (which is exactly how 
the proposed patch is getting CFLAGS in).

Unfortunately, batch file argument parsing is pretty horrid. I'd be happy to 
move to PowerShell based scripts, but that'll be asking a lot of some people, 
and probably isn't feasible for the existing buildbots.

Another concern about using CFLAGS is people ending up with broken builds 
because they had something else set in there - mostly because it's near 
impossible to diagnose remotely.

If we call it PY_CFLAGS< move it to pyproject.props, and require 
"$(BuildForRelease) != 'true'", then I'm fine with it. (The last condition 
ensures that official release builds via Tools\msi\buildrelease.bat will never 
be affected, and gives a fairly strong indication not to rely on implicit 
settings like this. Defaults that we need for actual releases should be 
integrated properly.)

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[issue24973] CFLAGS for Visual Studio

[Chris Hogan]

New submission from Chris Hogan:

This Visual Studio project change appends to the compiler flags any values in 
the CFLAGS environment variable.

--
components: Build, Windows
files: addcflags3_5.patch
keywords: patch
messages: 249427
nosy: christopher.hogan, paul.moore, r.david.murray, steve.dower, tim.golden, 
zach.ware
priority: normal
severity: normal
status: open
title: CFLAGS for Visual Studio
versions: Python 2.7, Python 3.5
Added file: http://bugs.python.org/file40308/addcflags3_5.patch

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[issue24973] CFLAGS for Visual Studio

[Chris Hogan]

Changes by Chris Hogan :


Added file: http://bugs.python.org/file40309/addcflags2_7.patch

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[issue24973] CFLAGS for Visual Studio

[Steve Dower]

Steve Dower added the comment:

The patch should just set it once in pyproject.props, not in each project.

Why is this necessary? Is there an option we should be exposing in some other 
way?

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[issue24973] CFLAGS for Visual Studio

[Zachary Ware]

Zachary Ware added the comment:

The real driver for this is having a nice easy way to pass '/fp:strict' to 
icl.exe (ICC's cl.exe).  There may be other things that would be nice to be 
able to pass easily for customization.

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[issue24973] CFLAGS for Visual Studio

[Zachary Ware]

Changes by Zachary Ware :


--
stage:  -> patch review
type:  -> enhancement
versions: +Python 3.6

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[issue24973] CFLAGS for Visual Studio

[Steve Dower]

Steve Dower added the comment:

I assume you're referring to #24974? The default (for MSVC) is /fp:precise, 
which should allow fenv_access, but maybe ICL uses /fp:fast by default for the 
extra speed?

It's not a safe 3.5 change now, but compiling with /fp:fast by default and 
using #pragma float_control(precise, push)/#pragma float_control(pop) around 
that section may be an option for 3.6, if the benchmarks show some value in it. 
Either way, the pragma is probably the better way to require particular 
behaviour for that section of code, rather than changing a global option.

I'm not totally opposed to allowing an extra option for setting flags when 
building, but there'll almost always be a better fix.

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[issue24973] CFLAGS for Visual Studio

[Zachary Ware]

Zachary Ware added the comment:

Steve Dower wrote:
> I assume you're referring to #24974?

It's somewhat related, yes, but I didn't intend for the two issues to be 
tightly coupled.  Both should be dealt with independently of each other.

> The default (for MSVC) is /fp:precise, which should allow
> fenv_access, but maybe ICL uses /fp:fast by default for the extra
> speed?

I believe that's correct.

> I'm not totally opposed to allowing an extra option for setting flags
> when building, but there'll almost always be a better fix.

That's probably true.  I will say though that it's really hard to pass build 
options to a buildbot.  I have yet to find a way to pass properties with no 
spaces in the value, for example, "/p:IncludeSSL=false" (if you know of a way 
to pass that to MSBuild correctly through Tools/buildbot/build.bat called by 
2.7's subprocess module, I'm all ears :)).  To continue the floating point 
example, the only method (other than this) I've found to pass in a different 
model is to hack in another property to check and set FloatingPointModel in the 
ClCompile ItemDefinitionGroup, which has the same problem as the 'IncludeSSL' 
issue I mentioned above.  With a nice simple 'CFLAGS' property that doesn't 
care about extra spaces in the value, it becomes possible to pass '/fp:strict' 
to a buildbot easily.

Also, ICC has *a lot* of extra command line options that may be interesting to 
pass in, but I'm quite sure we don't want to hack any of them into the project 
files.

By the way, '/fp:strict' is just what we've been manually defaulting to for ICC 
builds since before issue21167 was committed, which made '/fp:strict' 
unnecessary.

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